The present invention relates to a process for obtaining sorbitol and gluconic acid or gluconate from aqueous glucose/fructose mixtures by conversion in the presence of permeabilized cells of Zymomonas mobilis, and also to cells which can be used for the process.
It is known that sorbitol and gluconic acid or gluconate are produced in aqueous glucose/fructose mixtures enzymatically using glucose dehydrogenase and sorbitol dehydrogenase in the simultaneous presence of cofactors. Continuous addition or regeneration of the cofactors is a requirement for this process.
Thus, a process for the microbial conversion of glucose and fructose in aqueous solution using bacteria containing glucose/fructose transhydrogenase and, in particular, Zymomonas mobilis, has already been developed and is described in U.S. Pat. No. 4,755,467. This process uses desalted cell-free extracts, immobilized cells or non-growing cells which have been washed with phosphate, free buffer and which have, where appropriate, been permeabilized by a toluene treatment in 10% strength (v/v) toluene solution. As an alternative, gluconate kinase-negative mutants are produced and used.
Although a toluene treatment of this type results in premeabilized cells which are very useful for the desired fermentation, it appears non-optimal to use such considerable quantities of tulene for the permeabilization, ant there also appears to be a considerable risk that toluene residues may remain in the cell material.